Percent Yield Formula and Definition: The Complete Guide

Percent yield or percentage yield is the ratio of the actual yield and the theoretical yield of a chemical reaction. The experimental yield is divided by the theoretical yield and multiplied by 100 to be calculated as the percent yield. If the theoretical yield and the experimental yield are same then the percent yield will be 100%. But the percent yield is always lesser than 100% because the actual yield in the reaction is often less than the value of theoretical yield. Quite number of things like incomplete reaction and loss of sample or reactant can be reasonable for this. It is also happens that the yield percent is more than 100% and that means more product is recovered from a reaction than was predicted before. This thing can happen when other reactions are occurring at the same place are forming the same compound. Percent yield always holds a positive value.

It often happens that whenever you or someone else from your home cooks for your family members, first of all they calculate the exact number of the family member who will be eating the meal. Then the total amount of ingredients that is going to be used for making the food is calculated; so that everyone from the family can have the same amount of food. However sometimes this number can be messed up and you might end up with a wrong amount of food. And quite number of things can be reasonable for this miss calculation for example: food spillage while cooking, leaving the food on the oven for a long time, wrong measurements of the ingredients etc.

So you guys might be thinking that why the hell I am talking about cooking and all instead of the yield definition? Are you?

Well; I drew your attention there because I want to represent a clear concept of the main topic in front you.

Just like the cooking purposes; same thing also happens while making a compound in the chemistry labs. First of all we measure the reactants so that we can have a clear idea of how much compound we will be ending with. However these experimental measurements are made under ideal conditions; so it does not include the experimental errors. And you might be ended up with a amount which is bit different from the amount you have pretended before.

In chemistry we use a term called theoretical yield; which is the amount of component that is being calculated from the limiting reactant. 

Do you have a question in your mind? What is limiting reactant?

The limiting reactant is the amount of reactant that predicts the amount of main compound that can be formed from the reaction. The actual yield is the amount of compound produced when the reaction is over.

Formula of the Percentage yield

The main formula to calculate the percent yield is as follows:

Percent yield = (actual yield/theoretical yield) x 100

Key points

  • Actual yield is the amount of main product that is recovered from the chemical reaction
  • And theoretical yield is the amount of product received from the balanced reaction by using the limiting reactant.

You need to remember one more thing that the unit of both the theoretical and actual yield is needed to be the same.

Important Examples

So guys let’s look after some examples to clear out the concept.


If the magnesium carbonate decomposes and produces 15 grams of magnesium oxide. If the theoretical yield is taken to be 19 grams then what is the yield percentage of MgO?

The process to calculate the percent yield is really very easy if you know the exact value of the actual and theoretical yield. All you have to do is to put the values into the formula.

                    MgCO3 ——–> MgO + CO2

Percent yield = actual yield/theoretical yield x 100

                         = 15g/19g x 100

                         = 79%

So the percent yield of the reaction is 79%


Lets solve an another problem. In a chemical reaction if the calcium carbonate produces 15 grams of CaO. What is yield percent of the reaction?

                   CaCO3———> CaO + CO2

In the above reaction actual yield is given 15 grams

30 g x 1 mol CaCO3/100g x 1mol CaO/1 mol CaCO3 x 56g CaO/ 1 mol CaO

= 16.8g CaO

So the theoretical yield is 16.8g of CaO

Percent yield = actual yield/theoretical yield x 100

                         = 15g/16.8 x 100

                         =89.285 %

The percent yield of the reaction is 89.285%

Final lines

So here I have given the definition and the formula of the percent yield or percentage yield. I have also tried to make a clear concept of the topic through some useful examples for my lovely audience. I hope this will help you a lot.

So if you love this post then please put your valuable comments and also don’t forget to let me know that if I have missed out something important through the comment section. I will try to work on your problem as early as possible.

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